Keyless chucks used on electric power drills and similar tools typically have impacting lugs which are brought into engagement to restrain rotation of the split nut in the chuck so that continued rotation of the body will move the jaws relative to the split nut to move the chuck jaws in the opening or closing direction, depending upon the direction of rotation of the chuck body. Typically, the impacting faces on the impacting lugs are inclined to the axis of the chuck at a different angle depending upon whether it is opening or closing the jaws. The impact angle is greater in the opening direction than in the closing direction, thus ensuring the force which can be delivered to open the jaws will always be greater than that which will be delivered to close the jaws. In theory this means it will always be possible to open the jaws to remove the tool. The drawback with this arrangement is possibility to drive the jaws open into wedging contact with the chuck body with such force that the force available in the closing direction cannot free the jaws.
The object of this invention is to solve this problem.